1. Field of the Invention
The present invention relates to a superconducting laminated oxide substrate that can be used as the substrate of electronic devices such as superconducting devices, and a method of producing the same, and a method of producing a superconducting integrated circuit.
This application is based on Japanese Patent Applications (Japanese Patent Application No. Hei 11-252309 and Japanese Patent Application No. Hei 11-277616) filed in Japan, the contents of which are incorporated herein as a part of this specification.
2. Background Art
Use of a superconducting material generally makes it possible to decrease the high-frequency surface resistivity and operate a super conducting tunnel effect device at a high speed with lower power consumption. Thus attempts have been made to apply superconducting materials having such characteristics to electronic devices comprising high-frequency circuits. Super conducting electronic devices made of superconducting materials include superconducting integrated circuits. Superconducting integrated circuits are made by forming wiring consisting of a superconducting thin film via an insulation layer on a super conducting crystal substrate made of a superconducting oxide single crystal or a superconducting oxide polycrystal of Yxe2x80x94Baxe2x80x94Cuxe2x80x94O.
With the method of the prior art, superconducting integrated circuits of the constitution described above have been made by a process in which a rod of the superconducting oxide single crystal or superconducting oxide polycrystal of Yxe2x80x94Baxe2x80x94Cuxe2x80x94O is formed by a withdrawal method, and a superconducting oxide crystal substrate having a sheet shape, having a high degree of flatness, is made by slicing the rod and polishing, then forming an insulation film and a superconducting thin film on the superconducting oxide crystal substrate by a chemical vapor phase deposition process (CVD process), and forming the pattern of a superconducting circuit by photolithography process. The substrate is also heated as required, in order to improve the superconducting characteristics of the superconducting thin film that constitutes the superconducting circuit such as the critical current density.
The method of producing a superconducting integrated circuit of the prior art, however, involves heat treatment wherein the substrate is heated when forming the insulation film or the superconducting thin film for the circuit on the superconducting oxide crystal substrate, or heat treatment for heating the substrate to improve the superconducting characteristics. There has been the problem that thermal stress generated by the heat treatment, mechanical shock in a handling time, or the like, tends to cause defects such as cracks in the superconducting substrate resulting in a low production yield.
The problem described above becomes conspicuous particularly when producing superconducting integrated circuits of large sizes.
An object of the present invention is to achieve at least one of the goals of preventing cracks from occurring in the superconducting oxide crystal substrate due to the heat treatment conducted for the purpose of forming an insulation film or a conductor film on the superconducting oxide crystal substrate or a dielectric substrate that has a high degree of flatness and high degree of crystallinity and is used as the substrate of an electronic device whereon the insulation film and the conductive film to form a circuit are formed, and to provide easy connectivity between electrodes and wiring formed on substrates located at upper and lower positions.
In order to achieve the objects described above, the present invention provides a superconducting laminated oxide substrate comprising a laminate of a layer of a superconducting oxide crystal substrate made of a superconducting oxide single crystal or a superconducting oxide polycrystal, and a layer of a reinforcing crystal substrate.
The first aspect of the present invention employs a superconducting laminated oxide substrate formed by thermal compression bonding of the superconducting oxide crystal substrate consisting of a superconducting oxide single crystal or a superconducting oxide polycrystal and the reinforcing crystal substrate.
As a means of producing the superconducting laminated oxide substrate of the first aspect of the present invention, there is employed a method of producing a superconducting laminated oxide substrate, which comprises bringing a superconducting oxide crystal substrate made of a superconducting oxide single crystal or a superconducting oxide polycrystal into contact with a reinforcing crystal substrate and subjecting them to heat treatment, thereby bonding said superconducting oxide crystal substrate and said reinforcing crystal substrate on the interface thereof.
As a means of producing the superconducting laminated oxide substrate of the first aspect of the present invention, there is employed a method of producing a superconducting laminated oxide substrate, which comprises sandwiching a superconducting oxide crystal substrate made of a superconducting oxide single crystal or a superconducting oxide polycrystal by reinforcing crystal substrates on both sides thereof, subjecting to a heat treatment, thereby bonding the reinforcing crystal substrates onto both surfaces of the superconducting oxide crystal substrate, and slicing the superconducting oxide crystal substrate along a plane parallel to the surface.
In order to achieve the object described above, in the second aspect of the present invention, there may be employed a superconducting laminated oxide substrate according to claim 1, wherein the superconducting oxide crystal substrate made of the superconducting oxide single crystal or superconducting oxide polycrystal and the reinforcing crystal substrate are bonded by thermal compression.
As the method of producing the superconducting laminated oxide substrate of the second aspect of the present invention, there is employed a method of producing a superconducting laminated oxide substrate, which comprises bringing a superconducting oxide crystal substrate made of a superconducting oxide single crystal or a superconducting oxide polycrystal into contact with a superconducting thin oxide film of a reinforcing crystal substrate having the superconducting thin oxide film formed on the surface thereof and subjecting to a heat treatment, thereby bonding said superconducting oxide crystal substrate and said superconducting thin oxide film on the interface thereof.
In order to achieve the object described above, the third aspect of the present invention employs a superconducting laminated oxide substrate made by bonding the superconducting oxide crystal substrate consisting of a superconducting oxide single crystal or a superconducting oxide polycrystal and the reinforcing crystal substrate via an intermediate layer consisting of one or more layers, while at least the outermost layer of the intermediate layer is made of a low melting point material that melts at a temperature lower than the decomposition temperature of the superconducting oxide single crystal or the superconducting oxide polycrystal that constitutes the superconducting oxide crystal substrate.
As the method of producing the superconducting laminated oxide substrate of the third aspect of the present invention, there is employed a method of producing a superconducting laminated oxide substrate, which comprises disposing an intermediate layer having, at least in the outermost layer thereof, a low melting point layer that is made of a low melting-point material which melts at a temperature lower than the decomposition temperature of superconducting oxide single crystal or superconducting oxide polycrystal that constitutes a superconducting oxide crystal substrate between the superconducting oxide crystal substrate consisting of the superconducting oxide single crystal or the superconducting oxide polycrystal and a reinforcing crystal substrate, and applying a heat treatment to fuse the low melting point layer of said intermediate layer, thereby bonding said superconducting oxide crystal substrate and said reinforcing crystal substrate.
As the method of producing the superconducting laminated oxide substrate of the third aspect of the present invention, there may be employed a method of producing a superconducting laminated oxide substrate, which comprises applying a paste, that includes a material having melting point lower than the decomposition temperature of superconducting oxide single crystal or superconducting oxide polycrystal that constitutes a superconducting oxide crystal substrate as a major component, to at least one of the opposing surfaces of the superconducting oxide crystal substrate made of the superconducting oxide single crystal or the superconducting oxide polycrystal and a reinforcing crystal substrate, laminating said superconducting oxide crystal substrate on said reinforcing crystal substrate via the paste, and subjecting to a heat treatment, thereby to bond said superconducting oxide crystal substrate and said reinforcing crystal substrate.
Further, as the method of producing the superconducting laminated oxide substrate having any one of the constitutions described above, there may be employed a method of producing a superconducting laminated oxide substrate, which comprises applying a paste, that includes a low melting point material which melts at a temperature lower than the decomposition temperature of a superconducting oxide single crystal or a superconducting oxide polycrystal that constitutes a superconducting oxide crystal substrate as the major component, to both sides of said superconducting oxide crystal substrate made of the superconducting oxide single crystal or the superconducting oxide polycrystal by the withdrawal method, sandwiching said superconducting oxide crystal substrate by reinforcing crystal substrates via the paste on both sides thereof, subjecting to a heat treatment under a load, thereby bonding said reinforcing crystal substrates on both sides of said superconducting oxide crystal substrate, and slicing the superconducting oxide crystal substrate along a plane parallel to the surface thereof.
In the method of producing the superconducting integrated circuit according to the present invention, a thin dielectric film and a superconducting thin oxide film are formed on the superconducting laminated oxide substrate produced by the method of producing the superconducting laminated oxide substrate of one of the constitutions described above, and then the superconducting thin oxide film is patterned into wiring configuration, thereby forming the superconducting oxide wiring.
According to the method of producing the superconducting integrated circuit of the present invention, after forming the insulation film and the superconducting thin oxide film on at least one of the first and second superconducting laminated oxide substrates made by forming the superconducting oxide wiring from the superconducting oxide single crystal or the superconducting oxide polycrystal on the dielectric substrate, the superconducting thin oxide film is patterned into a wiring configuration to thereby form a superconducting oxide circuit, and then the superconducting oxide wiring of the first and second superconducting laminated oxide substrates are brought into contact directly with each other or via the superconducting thin oxide film and subjected to heat treatment, thereby bonding the superconducting oxide wiring of the first and second superconducting laminated oxide substrates with each other.
The superconducting thin oxide film, the superconducting oxide single crystal and the superconducting oxide polycrystal in the present invention refer not only to those having superconducting properties but also to those that develop superconducting properties when subjected to heat treatment.
Since the superconducting laminated oxide substrate of the present invention is, as a resulting of having the constitution described above, capable of improving the strength of the superconducting oxide crystal substrate that has a high degree of flatness and high crystallinity, the occurrence of cracks in the superconducting oxide crystal substrate can be greatly reduced and the production yield in the electronic device manufacturing process can be greatly improved even when heat treatment is applied when forming the insulation film and/or the conductor film on the laminated substrate.
Also because the superconducting oxide crystal substrate of the superconducting laminated oxide substrate has a high degree of flatness and high crystallinity, surface unevenness is unlikely to occur in the insulation film, wiring and electrodes that are formed on the superconducting oxide crystal substrate. Therefore, when two superconducting laminated oxide substrates whereon the insulation film, the wiring and the electrodes are formed are disposed to oppose each other and subjected to heat treatment, the electrodes and the wiring disposed at the upper position and lower position can be easily connected.
Also according to the method of producing the superconducting laminated oxide substrate of the present invention, the superconducting laminated oxide substrate of the present invention can be preferably obtained due to the constitution described above.
Also according to the method of producing the superconducting integrated circuit of the present invention, since the superconducting thin oxide film is patterned into the wiring configuration to form the superconducting oxide wiring after forming the thin dielectric film and the superconducting thin oxide film on the superconducting laminated oxide substrate produced by the method of the present invention, the occurrence of cracks in the superconducting oxide crystal substrate can be greatly reduced and the production yield in the electronic device manufacturing process can be greatly improved even when the heat treatment is applied when forming the insulation film and/or the conductor film.
Also according to the method of producing the superconducting integrated circuit of the present invention, the wiring of the first and second superconducting laminated oxide substrates can be easily connected, since the insulation film and the superconducting thin oxide film are formed on at least one of the first and second superconducting laminated oxide substrates made by forming the superconducting oxide wiring from superconducting oxide single crystal or superconducting oxide polycrystal on the dielectric substrate, the superconducting thin oxide film is patterned into a wiring configuration to thereby form the superconducting oxide circuit, and then the superconducting oxide wiring of the first and second superconducting laminated oxide substrates are brought into contact directly with each other or via the superconducting thin oxide film and subjected to heat treatment, thereby fusing the superconducting oxide wirings of the first and second superconducting laminated oxide substrates with each other.